OPTICAL WAVEFRONT MEASURING DEVICE AND METHOD
In an optical wavefront measuring device, a SLM generates a plurality of different through holes, so that light beams pass through the through holes and form a plurality of light patterns. The distance between an infinite objective lens module and a test lens is adjusted so that the light patterns enter into a wavefront sensor in the form of approximately parallel light after passing through the infinite objective lens module and the test lens. The wavefront sensor captures a plurality of WS images which do not have a fold-over phenomenon according to the light patterns. Computer by using an algorithm to obtain wavefront change information, and then reconstructs a wavefront on the basis of the wavefront change information.
This application claims priority of No. 104138552 filed in Taiwan R.O.C. on Nov. 20, 2015 under 35 USC 119, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTIONField of the Invention
The present invention relates to an optical wavefront measuring device and a method thereof, and more particularly to an optical wavefront measuring device and a method thereof using a SLM generates and a wavefront stitching technique to prevent light spots from generating a fold-over and to rebuild a wavefront having high aberration.
Related Art
Taking into consideration a large number of lenses are used in a variety of optical products, the skilled artisans pay a great deal of attention to how to quickly and accurately detect the optical quality of the lens. The wavefront of a lightwave is the locus of points characterized by propagation of position of the same phase, that is, the points have the same propagation distances from the light source generating the lightwave. Shack-Hartmann wavefront sensor (SHWS), as disclosed by U.S. Pat. No. 4,141,652, has advantages of low cost, simple structure, high measurement speed and low requirements for environmental vibration, so that it has been used in wavefront measuring.
According to the Shack-Hartmann wavefront sensor 100, the lateral variations of wavefront are equal to the lateral offset of spots divided by the focal length of the lens. Then, the Zernike polynomial may be used to rebuild the wavefront. More specifically, Zernike polynomial coefficients are obtained in advanced, and then the coefficients are substituted into the Zernike polynomial to rebuild the wavefront. Regarding to the algorithm, [“History and principle of Shack-Hartmann Wavefront Sensing,” Refractive Surgery Journal, September/October, 2001, Vol. 17] and [“Modal wavefront estimation from phase derivative measurements,” J. Opt. Soc. Am. July, 1979, Vol. 69, Issue 7, pp. 972-977] are listed for the purpose of reference.
However, a general optical element, such as lens, or system whose pupil is circular and whose related properties is distributed symmetrically to the axis, so that when the techniques are applied to aspherical lens, there is still room for improvement. In order to effectively solve the problem of identification of lateral offset under large phase difference, we provide an improved optical wavefront measuring device and method which are suitable for measuring the wavefront of an optical lens or system having a large phase difference.
SUMMARY OF THE INVENTIONAn objective of the present invention is to provide an optical wavefront measuring device and method. Another objective of the present invention is to provide an optical wavefront measuring device and method using a SLM generates and a wavefront stitching technique to prevent light spots from generating a fold-over and to rebuild a wavefront having high aberration.
According to one embodiment of the present invention, an optical wavefront measuring device for testing a lens under test comprises a spatial light modulator (SLM), a wavefront sensor, an infinite objective lens module and a computer. The SLM is used to produce different apertures, whereby different light beams passing through the different apertures form light patterns. The infinite objective lens module is used to adjust the distance between the infinite objective lens module and the lens under test, whereby the light patterns passing through the lens under test and the infinite objective lens module become approximately parallel and then enter into the wavefront sensor. The wavefront sensor is used to capture WS images on the basis of the light patterns, wherein the WS images do not have a fold-over phenomenon. The computer is used to stitch the WS images by using an algorithm to obtain a wavefront variation information, and then to rebuild a complete wavefront on the basis of the wavefront variation information.
In one embodiment, the optical wavefront measuring device further comprises a parallel light source system used for generating the light beams being parallel.
In one embodiment, the infinite objective lens module comprises an infinite objective lens and an actuator. The light patterns sequentially pass through the infinite objective lens module and the lens under test. The light patterns passing through the infinite objective lens form a plurality of focused spots. The actuator is used to adjust the distance between the infinite objective lens and the lens under test, so that the focused spots are focused at the focal length of the lens under test.
In one embodiment, the infinite objective lens module comprises an infinite objective lens and an actuator. The light patterns sequentially pass through the lens under test and the infinite objective lens module. The light patterns passing through the lens under test form a plurality of focused spots. The actuator is used to adjust the distance between the infinite objective lens and the lens under test, so that the focused spots are focused at the focal length of the infinite objective lens.
In one embodiment, the algorithm is a phase stitching algorithm (PSA), a gradient stitching algorithm (GSA) or a least-square fitting (LSF).
In one embodiment, the apertures include a circular aperture and a first annular aperture being concentric with each other. In one embodiment, the inside diameter of the first annular aperture is not larger than the diameter of the circular aperture. In one embodiment, the apertures further include a second annular aperture being concentric with the first annular aperture. The inside diameter of the second annular aperture is not larger than the outside diameter of the first annular aperture.
According to one embodiment of the present invention, an optical wavefront measuring method for testing a lens under test, the method comprising: using a SLM to produce different apertures, whereby different light beams passing through the different apertures form a plurality of light patterns; using an infinite objective lens module to adjust the distance between the infinite objective lens module and the lens under test, whereby the light patterns passing through the lens under test and the infinite objective lens module become approximately parallel and then enter into a wavefront sensor; using a wavefront sensor to capture a plurality of WS images on the basis of the light patterns, wherein the WS images do not have a fold-over phenomenon; and using a computer to stitch the WS images by using an algorithm to obtain a wavefront variation information, and then to rebuild a complete wavefront on the basis of the wavefront variation information.
In one embodiment, the apertures include a circular aperture and a first annular aperture being concentric with each other. The step of using a SLM to produce different apertures comprises: increasing the diameter of the circular aperture by increments of Δr at each step until n-th step at which the WS image corresponding to the circular aperture has a fold-over phenomenon, and setting the diameter of the circular aperture to be the diameter φn-1 at (n-1)-th step; setting the inside diameter A0 of the first annular aperture to be not larger than the diameter φn-1 of the circular aperture; and increasing the outside diameter of the first annular aperture by increments of Δr at each step until i-th step at which the WS image corresponding to the first annular aperture has a fold-over phenomenon, and setting the outside diameter of the first annular to be the diameter Ai-1 at (i-1)-th step.
In one embodiment, the apertures further include a second annular aperture being concentric with the first annular aperture. The step of using a SLM to produce different apertures further comprises: setting the inside diameter 2A0 of the second annular aperture to be not larger than the outside diameter A of the first annular aperture, and increasing the outside diameter of the second annular aperture by increments of Δr at each step until I-th step at which the WS image corresponding to the second annular aperture has a fold-over phenomenon, and setting the outside diameter of the second annular to be the diameter 2AI-1 at (I-1)-th step.
In one embodiment, the algorithm is a phase stitching algorithm (PSA), a gradient stitching algorithm (GSA) or a least-square fitting (LSF).
According to one embodiment of the present invention, different WS images without a fold-over phenomenon are obtained; the wavefronts from the WS images are stitched; the wavefront aberrations after stitching are obtained; then a complete wavefront can be rebuilt. As a result, the problem of the fold-over phenomenon can be resolved, which occurs under high aberrations due to lateral displacement, so that the optical wavefront measuring device and method of the present invention are suitable for testing an aspherical lens.
The foregoing features, aspects, and advantages of the present disclosure will now be described with reference to the drawings of preferred embodiments that are intended to illustrate and not to limit the disclosure.
These and other embodiments of the present disclosure will also become readily apparent to those skilled in the art from the following detailed description of preferred embodiments having reference to the attached figures; however, the disclosure is not limited to any particular embodiment(s) disclosed herein. Accordingly, the scope of the present disclosure is intended to be defined only by reference to the appended claims.
After the light patterns pass through the infinite objective lens module 220 and lens under test 300, a WS (wavefront sensor) image is formed in the wavefront sensor 230. The wavefront sensor 230 captures the WS image and transmits it to the computer 240. The light pattern would be focused by the infinite objective lens module 220 and lens under test 300 to form a focused spot 223. The distance between the focused spot 223 (or the infinite objective lens module 220) and the lens under test 300 is adjusted, so that the light pattern can enter into the wavefront sensor 230 in a form of parallel light. The computer 240 performs wavefront calculation on the WS images to obtain a desired wavefront.
More specifically, in the embodiment of
The wavefront sensor 230 comprises a lens array 231 and an image sensor 232. After passing through the lens array 231, the light pattern enters into the image sensor 232. The image sensor 232 obtains the WS image and then transmits it into the computer 240.
the computer 240 is used to control the SLM 210, the infinite objective lens module 220 and the wavefront sensor 230, to capture the WS image, to adjust the focal length, to analyze the spots folded over, to conduct stitching (described later), to perform wavefront calculation on the WS images, so that a desired wavefront can be obtained.
The stitching method used to solve the problem that spots fold over will be described in the following.
During the processes, if the SLM 210 increases the diameter of the aperture at a certain step where there is not a change between the former and latter WS images, one can confirm that the lens 300 has the biggest pupil at that certain step and then stops increasing the diameter of the aperture.
During the processes, if the SLM 210 increases the outside diameter of the first annular aperture at a certain step where there is not a change between the former and latter WS images, one can confirm that the lens 300 has the biggest pupil at that certain step and then stops increasing the outside diameter. In an embodiment, the inside diameter A0 may be smaller than diameter φn-1. For example, A0=φn-1−m*Δr. The value of m corresponds to the size of the overlap region and may be determined by the kind of the stitching technique. When m=0, there is not an overlap region.
During the processes, if the SLM 210 increases the outside diameter of the second annular aperture at a certain step where there is not a change between the 2AI and 2AI-1 WS images, it is confirmed that the lens 300 has the biggest pupil at that certain step and then stops increasing the outside diameter. In an embodiment, the inside diameter 2A0 is smaller than the outside diameter Ai-1 of the first annular aperture. For example, 2A0=Ai-1−m*Δr. The value of m corresponds to the size of the overlap region and may be determined by the kind of the stitching technique. When m=0, there is not an overlap region.
Finally, the wavefront of the whole pupil is rebuilded, as shown in
An optical wavefront measuring method according to an embodiment of the present invention will be described in the following.
As shown in
Finally, steps S05˜08 are repeated to obtain a plurality of annular WS images having different sizes and record them (Step S09). When the WS images have not a fold-over phenomenon and there is not a change between the xAz and xAz-1 WS images, the method goes to next step S10. Wavefront calculations are performed on the φn-1, Ai-1, . . . , and xAz-1 WS images and then the wavefronts from the WS images are stitched together to rebuild a complete wavefront of the whole pupil.
As above, according to an embodiment of the present invention, different WS images without a fold-over phenomenon are obtained; the wavefronts from the WS images are stitched; the wavefront aberrations after stitching are obtained; then a complete wavefront can be rebuilt. As a result, the problem of the fold-over phenomenon can be resolved, which occurs under high aberrations due to lateral displacement, so that the optical wavefront measuring device and method of the present invention are suitable for testing an aspherical lens.
Claims
1. An optical wavefront measuring device for testing a lens under test, comprising a spatial light modulator (SLM), a wavefront sensor, an infinite objective lens module and a computer, wherein
- the SLM is used to produce different apertures, whereby different light beams passing through the apertures form a plurality of light patterns,
- the infinite objective lens module is used to adjust the distance between the infinite objective lens module and the lens under test, whereby the light patterns passing through the lens under test and the infinite objective lens module become approximately parallel and then enter into the wavefront sensor,
- the wavefront sensor is used to capture a plurality of WS images on the basis of the light patterns, wherein the WS images do not have a fold-over phenomenon, and
- the computer is used to stitch the WS images by using an algorithm to obtain a wavefront variation information, and then to rebuild a complete wavefront on the basis of the wavefront variation information.
2. The optical wavefront measuring device according to claim 1, further comprising a parallel light source system used for generating the light beams being parallel.
3. The optical wavefront measuring device according to claim 1, wherein
- the infinite objective lens module comprises an infinite objective lens and an actuator,
- the light patterns sequentially pass through the infinite objective lens module and the lens under test,
- the light patterns passing through the infinite objective lens form a plurality of focused spots, and
- the actuator is used to adjust the distance between the infinite objective lens and the lens under test, so that the focused spots are focused at the focal length of the lens under test.
4. The optical wavefront measuring device according to claim 1, wherein
- the infinite objective lens module comprises an infinite objective lens and an actuator,
- the light patterns sequentially pass through the lens under test and the infinite objective lens module,
- the light patterns passing through the lens under test form a plurality of focused spots, and
- the actuator is used to adjust the distance between the infinite objective lens and the lens under test, so that the focused spots are focused at the focal length of the infinite objective lens.
5. The optical wavefront measuring device according to claim 1, wherein the algorithm is a phase stitching algorithm (PSA), a gradient stitching algorithm (GSA) or a least-square fitting (LSF).
6. The optical wavefront measuring device according to claim 1, wherein
- the apertures include a circular aperture and a first annular aperture being concentric with each other, and
- the inside diameter of the first annular aperture is not larger than the diameter of the circular aperture.
7. The optical wavefront measuring device according to claim 6, wherein
- the apertures further include a second annular aperture being concentric with the first annular aperture, and
- the inside diameter of the second annular aperture is not larger than the outside diameter of the first annular aperture.
8. An optical wavefront measuring method for testing a lens under test, the method comprising:
- using a SLM to produce different apertures, whereby different light beams passing through the apertures form a plurality of light patterns;
- using an infinite objective lens module to adjust the distance between the infinite objective lens module and the lens under test, whereby the light patterns passing through the lens under test and the infinite objective lens module become approximately parallel and then enter into a wavefront sensor;
- using the wavefront sensor to capture a plurality of WS images on the basis of the light patterns, wherein the WS images do not have a fold-over phenomenon; and
- using a computer to stitch the WS images by using an algorithm to obtain a wavefront variation information, and then to rebuild a complete wavefront on the basis of the wavefront variation information.
9. The optical wavefront measuring method according to claim 8, wherein
- the apertures include a circular aperture and a first annular aperture being concentric with each other, and
- the step of using a SLM to produce different apertures comprises: increasing the diameter of the circular aperture by increments of Δr at each step until n-th step at which the WS image corresponding to the circular aperture has a fold-over phenomenon, and setting the diameter of the circular aperture to be the diameter φn-1 at (n-1)-th step, setting the inside diameter A0 of the first annular aperture to be not larger than the diameter φn-1 of the circular aperture, and
- increasing the outside diameter of the first annular aperture by increments of Δr at each step until i-th step at which the WS image corresponding to the first annular aperture has a fold-over phenomenon, and setting the outside diameter of the first annular to be the diameter Ai-1 at (i-1)-th step.
10. The optical wavefront measuring method according to claim 9, wherein the apertures further include a second annular aperture being concentric with the first annular aperture, and
- the step of using a SLM to produce different apertures further comprises:
- setting the inside diameter 2A0 of the second annular aperture to be not larger than the outside diameter A of the first annular aperture, and
- increasing the outside diameter of the second annular aperture by increments of Δr at each step until I-th step at which the WS image corresponding to the second annular aperture has a fold-over phenomenon, and setting the outside diameter of the second annular to be the diameter 2AI-1 at (I-1)-th step.
11. The optical wavefront measuring method according to claim 8, wherein the algorithm is a phase stitching algorithm (PSA), a gradient stitching algorithm (GSA) or a least-square fitting (LSF).
Type: Application
Filed: Oct 20, 2016
Publication Date: May 25, 2017
Inventor: Jen Sheng LIANG (Jubei City)
Application Number: 15/298,842